misfire on 4-5-6 bank after replacing head

[Coaster]

Well I'm stumped.

It's not the plugs or the coils. The shop says they touched all the connections to ensure they were clean and tight. They reviewed hours of PWIS files and the code still pops up randomly. Fuel trim on bank 2 seems a little higher than bank 1 but I'm no expert.

One theroy includes a small volumetric difference between the old head on 1-2-3 and new/used head 4-5-6 which is causing the system to see a difference on the 4-5-6 side.

Another theory says it's an electrical gremlin potentially tied to the under drive pulley. It's a perception that the fault occurs at or near idle and the under drive pulley doesn't create enough voltage (perhaps from a tired alternator) and then the CEL goes off.

In the mean time I'd like to get a blue tooth OBDII reader that can be "permanently" installed and store scrolling data, once the CEL pops I can capture the data in the previous 5-10 mins via my ipad. Any suggestions until Fred's infotainment center is online?

[bwdz]

What does the freeze frame pull up? It might give you a hint as to what was happening when the code was triggered.

[Gelbster]

Originally Posted by bwdz

What does the freeze frame pull up? It might give you a hint as to what was happening when the code was triggered.

Now we are getting closer to diagnosis !
An old mechanic truism when faced with aberant problems is to return to stock (pulley) but that seems unlikely - but it is easy to try.
Whatever you do , be aware the DME may be slow to learn the new situation. We had an interesting Thread on such speculation recently. Doing a hard reset seemed to work.

Research carefully.

[Coaster]

Originally Posted by bwdz

What does the freeze frame pull up? It might give you a hint as to what was happening when the code was triggered.

Be gentle, I'm learning. What freeze frame? Can you explain this in simple terms. I don't have the data, the shop does. I'm looking for a blue tooth reader to record active data so maybe I can capture itat the moment it flashes.

[bwdz]

The freeze frame is an OBD function. It records data when the code is set. It can be accessed with even cheap code readers. It will show you the snapshot of the sensor data at the moment the code set. It will typically show the baro, o2 readings, ect, vehicle sensor speed, load etc.. etc... If there are multiple codes the freeze frame function will only remember one but sometimes up to 3 freeze frames on newer cars. It will keep the frame from what is considered the most important dtc. Essentially what you want to do is drive around and gather data to see what sets the code but your computer already has a snapshot of all the sensor data at the moment it threw the code. It is as if you took a picture of the sensor data feed the moment it decides to throw the code. There are possible clues in there.
If you are suspecting increased compression from the head replacement there is also a way to use a starting system oscilloscope that most garages have to look for clues. Disable the fuel and spark and hook it up. Crank the engine over. The wave form of starter current draw spikes on each compression stroke of each piston. If there are different heights in the spikes on 3 of the cylinders you will see that and by following the firing order you can make a guess that it relates to the 4 5 and 6. Essentially you are using the power that the starter must use as a compression tester. I use this to look for potential misfires when I suspect internal engine problems as it can hooked up in under a minute and requires no removal of anything on the car but a relay or fuse and it can find me a dead cylinder in seconds rather than pulling parts off a car.
I recently found a problem on a supercharged Cobalt in my shop using the freeze frame. The car had been to multiple shops and dealers and had the problem for over a year. It would run great but once a week or so would pop into limp mode for map correlation. The car was highly modified with different injectors and small sc pulley. Everytime someone diagnose it everything was fine, it would test drive fine once code was reset and all sensors were in spec. The freeze frame showed 0 volts on the SCIP sensor. The SCIP and Map were replaced several times by different shops and the car would run great for a few days and then the code would come back. By seeing the freeze frame with 0 volts I was able to determine that there must be an intermittent connection and sure enough if you wiggled the plug hard enough there was, so it worked 99.9% of the time but the freeze frame showed that it must have a bad connection.